The present invention concerns soft sealing materials which do not contain asbestos and other inorganic fibrous substances. More particularly it relates to new and improved non-woven sealing materials produced by means of paper processes or paper calendaring techniques from organic synthetic fibers, powdered graphite and polymeric binders. This invention also relates to the uses of these materials for the production of sealing materials for technical or industrial purposes, particularly such applications as seals or gaskets used in the construction of heating systems and also gaskets for use in the construction of chemical plants and power plants.
Asbestos, as well as all of the inorganic fibers lying within a certain fiber size distribution range, i.e., those having certain fiber lengths of between about 3 micrometers to about 5 micrometers (&gt;5/.mu.m, .phi.&lt;3/.mu.m, length/.phi.=3:1) are suspected of causing adverse effects injurious to health. In particular, health hazards associated with asbestos have been known for some time. The additional safety steps presently required for processing asbestos, as well as the other inorganic fibers, renders them uneconomical to use. Therefore, new materials which, if possible, do not contain the above-mentioned inorganic fibers are needed.
Conventional asbestos-free, soft-substance flat packing materials consist of either mixtures of various fiber kinds having mineral filler additives and organic binders (DE-PS 2914173 and DE-OS 3232255) or expanded graphite.
Fiber-free gaskets on the basis of expanded graphite are known. However, the expensive production difficulties resulting from their further processing prevent the success of these products on the market for lack of sufficient handling stability.
Developments using fiber-reinforced graphite are also known, for example, from U.S. Pat. No. 4,443,517. Prior gasket compositions employ organic binders in amounts of 3 to 8% which are necessary to obtain a sufficient cross-sectional tightness and for an economical manufacture. A total fiber content of about 6%, and more than 60% of flake graphite is used. This gasket formulation exhibits poor temperature stability in use.
Accordingly, it is an object of this invention to provide soft non-woven sealing materials, free of asbestos and other inorganic fibrous substances, having good temperature stability properties, which may be made in an ecologically beneficial manner using paper processes or paper calendaring techniques without the need for solvents or other offensive or corrosive chemicals or acids.
It is another object of the present invention to provide new and improved planar non-woven gasket materials useful in the production of special, highly stressed flat packings.